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A significant example of directional selection in populations is the fluctuations of light and dark phenotypes in peppered moths in the 1800s. [16] During the industrial revolution, environmental conditions were rapidly changing with the newfound emission of dark, black smoke from factories that would change the color of trees, rocks, and other ...
Examples: The thumb is on the radial side of the hand (the same as saying the lateral side); the ulnar side of the wrist is the side toward the little finger (medial side). Ventral and dorsal , which describe structures derived from the front (ventral) and back (dorsal) of the embryo , before limb rotation.
For example, structures may be described relative to the anterior superior iliac spine, the medial malleolus or the medial epicondyle. Anatomical lines are used to describe anatomical location. For example, the mid-clavicular line is used as part of the cardiac exam in medicine to feel the apex beat of the heart.
These terms come from the Latin words with the same meaning. [a] Flexion is a bending movement that decreases the angle between a segment and its proximal segment. [9] For example, bending the elbow, or clenching a hand into a fist, are examples of flexion. When a person is sitting down, the knees are flexed.
The notochord provides a directional reference to the surrounding tissue as a midline structure during embryonic development, acts as a precursor for vertebrae and a primitive axial endoskeleton. In aquatic animals it can facilitate tail motion when swimming. [1]
Most of the principal terms can be combined using their corresponding combining forms (such as mesio-for mesial and disto-for distal). They provide names for directions (vectors) and axes; for example, the coronoapical axis is the long axis of a tooth. Such combining yields terms such as those in the following list.
Chemotaxis refers to the directional migration of cells in response to chemical gradients; several variations of chemical-induced migration exist as listed below. Chemokinesis refers to an increase in cellular motility in response to chemicals in the surrounding environment. Unlike chemotaxis, the migration stimulated by chemokinesis lacks ...
Type 1 crosses the sagittal plane in the same brain region or spinal segment where the cell body is located. Examples are Mauthner cells in fish and amphibians. Type 2 crosses the sagittal plane in a different brain region. Example: pyramidal decussations. The first type is known also for invertebrates, whereas the second type only occurs in ...